(1) Field of the Invention:
This invention generally relates to a so-called passive seat belt system for protecting an occupant in the event of a vehicular emergency. More specifically, this invention is concerned with an assembly of a slider carrying a webbing fastened at one end thereof to the slider and being movable on and along a slide rail and an anchor latch device for holding the slider at an occupant-restraining position. In particular, this invention pertains to such a slider and anchor latch device assembly that the anchor latch device has strength and durability sufficient to withstand the considerable pulling force or tension which may be applied to the slider.
(2) Description of the Related Art:
A conventional passive seat belt system is illustrated by way of example in FIG. 11. A residual portion of an occupant-restraining webbing is wound into an inner retractor 200 provided on a lower side part of of a seat, while the free end of the webbing is fastened to a slider 40 via an emergency release buckle 50. The slider 40 is retained in a slide rail 30 mounted on a roofside area of the inner wall of the roof of a vehicle in such a way that the slider 40 can move back and forth along the longitudinal axis of the vehicle. The slider 40 is drawn along the slide rail by a drive member like a wire paid out or taken up by a drive unit 90 actuated by opening and closing the associated door. Internally the drive unit 90 has a reel connected to a motor, neither of which components is illustrated in the drawing. The drive member is wound on the reel, so that the drive member can be paid out or taken up.
An anchor latch device 85 is also provided at the rear end of the slide rail 30. Between the anchor latch device 85 and the drive unit 90, a guide tube 80 is arranged to guide the drive member therethrough.
Reference is now had to FIG. 12, which shows one example of conventional anchor latch devices employed in such passive seat belt systems.
A rear end portion of the slide rail 30, said end portion being located on a center pillar, is secured to the center pillar by bolts (not in illustration) via a bracket (also not shown). The rear end portion of the slide rail 30 is surrounded by a steel-made anchor base 20. The anchor base 20 is formed integrally with a mounting plate 26 (see FIG. 1). The mounting plate 26 is secured to the center pillar by bolts (not shown), so that the rear end portion of the slide rail 30 is also secured to the center pillar by way of the anchor base 20 and mounting plate 26.
The anchor latch device is now described in more detail. The anchor base 20 is pressed from high-strength sheet metal to press working. The anchor base 20 is formed to have a closed square shape in cross-section, so that it can surround the slide rail 30. A slider-receiving slot 28 is formed in a front wall 21 of the anchor base 20, said front wall 21 facing the emergency release buckle 50, so that the slot 28 downwardly terminates in an inner edge or end portion 22. When the slider 40 is driven downward, the inner edge portion 22 advances into an anchor-receiving slot 41 of the slider 40 so that the slider 40 is allowed to enter approximately to a longitudinal central portion of the anchor base 20.
On the other hand, the slider 40 defines an anchor-receiving slot 41 which allows the inner edge portion 22 of the front wall 21 of the anchor base 20, said front wall 21 facing the emergency release buckle 50, to advance into and engage the slider 40 when the slider 40 advances into the inside of the anchor base 20.
The anchor latch device operates in the following manner. When the passive seat belt system is in an occupant-restraining state, the anchor latch device maintains the anchor groove 41 of the slider 40 in engagement with the front wall 21 of the anchor base 20. Accordingly, the slider 40 is held in the anchor latch device.
Reference is now made to FIGS. 8-10. Assume that the passive seat belt system is in an occupant-restraining state and a vehicular emergency has occurred to exert a large tensile force to the webbing. In the anchor latch device of the passive seat belt system, the tensile force applied to the webbing is transmitted as a pulling force to the slider 40 and owing to the engagement between the anchor-receiving slot 41 of the slider 40 and the front wall 21 of the anchor base 20, the pulling force is borne by the front wall 21. Here, the line of action of the pulling force acting on the slider 40 is indicated by an arrow in FIG. 9. Since the line of action is not perpendicular to the plane of the front wall 21, the slider 40 is caused to tilt relative to the front wall 21 of the anchor base 20. As a result, a localized and concentrated load is applied to the inner edge portion 22 of front wall 21 of the anchor base 20. There is hence a potential danger that the thus-loaded part of the inner edge portion 22 may be torn up and the strength and durability of the anchor latch device may be reduced.